1. Field of the Invention
The present invention relates to an automatic digital variable resistor and a display device including the same, and more particularly, to an automatic digital variable resistor designed to prevent failure in a liquid crystal display (LCD) panel and an LCD having the same.
2. Description of the Related Art
A liquid crystal display (“LCD”) is a commonly used flat panel display and offers a variety of characteristics, including low power consumption, slim and lightweight design, a low driving voltage compared to other displays.
An LCD panel can include an upper panel with a common electrode and a color filter, a lower panel with a thin film transistor (“TFT”) and a pixel electrode, and a liquid crystal layer sandwiched between the upper panel and the lower panel. In the LCD, an electric field is created by applying different electric potentials to the pixel electrode and the common electrode, which alters arrangement of liquid crystal molecules to control the transmittance of light. In this way, the LCD displays a desired image.
The LCD can include the LCD panel, a driving voltage generator, a, gate driver, a gamma voltage generator, a data driver, and a timing controller.
The LCD panel includes a plurality of gate lines and a plurality of data lines intersecting the plurality of gate lines. The driving voltage generator produces a gate-on voltage, a gate-off voltage, and a common voltage. The gate driver is connected to the plurality of gate lines of the LCD panel and applies a gate signal including the gate-on voltage and the gate-off voltage to the plurality of gate lines. The gamma voltage generator produces two sets of gamma voltages, i.e., gamma voltages with positive and negative polarities, which are associated with a change in the transmittance of a unit pixel, and applies the gamma voltages to the LCD panel. The data driver is coupled to the plurality of data lines of the LCD panel, generates a plurality of gray scale voltages based on the plurality of gamma voltages received from the gamma voltage generator, selects gray scale voltages, and applies the selected gray scale voltages to each pixel as data signals.
The timing controller receives image data and input control signals controlling the display of the image data, such as vertical synchronization signal Vsync and horizontal synchronization signal Hsync, main clock MCLK and data enable signal DE, from an external graphic controller. The timing controller also generates a gate control signal and a data control signal in response to the input control signals, processes R, G, B image signals suitably according to the operation conditions of the LCD panel, and provides the gate control signal and the data control signal and the resulting image signals R′, G′, and B′ to the gate driver and the data driver, respectively.
The driving voltage generator includes a digital variable resistor generating a common voltage. The digital variable resistor includes a memory in which an intermediate value of n-bit data is initially stored. The digital variable resistor receives operating voltage VDD and control signal CTL, reads the intermediate value stored in the memory in response to the control signal CTL, and outputs an analog voltage corresponding to the intermediate data value.
However, when data is stored in the memory, the memory is reset to a maximum value of n-bit data instead of the intermediate value. Furthermore, even if the intermediate value of n-bit data is normally stored in the memory, the minimum or maximum value of n-bit data can be read from the memory when static electricity or read failure occurs. This may cause flickering on an LCD and may result in noise in gray scales.